The present invention relates to an artificial kidney system for use in providing dialysis. More particularly, the present invention is directed to a hemodialysis system incorporating one or more flow sensors which significantly improve hemodialysis safety so as to provide hemodialysis to a broader base of patients and to decrease the overall cost of hemodialysis.
Applicant(s) hereby incorporate herein by reference any and all patents and published patent applications cited or referred to in this application.
Hemodialysis is a medical procedure that is used to achieve the extracorporeal removal of waste products including creatine, urea, and free water from a patient's blood involving the diffusion of solutes across a semipermeable membrane. Failure to properly remove these waste products can result in renal failure.
During hemodialysis, the patient's blood is removed by an arterial line, treated by a dialysis machine, and returned to the body by a venous line. The dialysis machine includes a dialyzer containing a large number of hollow fibers forming a semipermeable membrane through which the blood is transported. In addition, the dialysis machine utilizes a dialysate liquid, containing the proper amounts of electrolytes and other essential constituents (such as glucose), that is also pumped through the dialyzer.
Typically, dialysate is prepared by mixing water with appropriate proportions of an acid concentrate and a bicarbonate concentrate. Preferably, the acid and the bicarbonate concentrate are separated until the final mixing right before use in the dialyzer as the calcium and magnesium in the acid concentrate will precipitate out when in contact with the high bicarbonate level in the bicarbonate concentrate. The dialysate may also include appropriate levels of sodium, potassium, chloride, and glucose.
The dialysis process across the membrane is achieved by a combination of diffusion and convection. The diffusion entails the migration of molecules by random motion from regions of high concentration to regions of low concentration. Meanwhile, convection entails the movement of solute typically in response to a difference in hydrostatic pressure. The fibers forming the semipermeable membrane separate the blood plasma from the dialysate and provide a large surface area for diffusion to take place which allows waste, including urea, potassium and phosphate, to permeate into the dialysate while preventing the transfer of larger molecules such as blood cells, polypeptides, and certain proteins into the dialysate.
Typically, the dialysate flows in the opposite direction to blood flow in the extracorporeal circuit. The countercurrent flow maintains the concentration gradient across the semipermeable membrane so as to increase the efficiency of the dialysis. In some instances, hemodialysis may provide for fluid removal, also referred to as ultrafiltration. Ultrafiltration is commonly accomplished by lowering the hydrostatic pressure of the dialysate compartment of a dialyzer, thus allowing water containing dissolved solutes including electrolytes and other permeable substances to move across the membrane from the blood plasma to the dialysate. In rarer circumstances, fluid in the dialysate flow path portion of the dialyzer is higher than the blood flow portion, causing fluid to move from the dialysate flow path to the blood flow path. This is commonly referred to as reverse ultrafiltration. Since ultrafiltration and reverse ultrafiltration can increase the risks to a patient, ultrafiltration and reverse ultrafiltration are typically conducted only while supervised by highly trained medical personnel.
Unfortunately, hemodialysis suffers from numerous drawbacks. An arteriovenous fistula is the most commonly recognized access point. To create a fistula, a doctor joins an artery and a vein together. Since this bypasses the patient's capillaries, blood flows rapidly. For each dialysis session, the fistula must be punctured with large needles to deliver blood into, and return blood from the dialyzer. Typically, this procedure is done three times a week and for 3-4 hours per each treatment. To a lesser extent, patients conduct hemodialysis at home. Home hemodialysis is typically done for two hours, six days a week. Home hemodialysis is considered less stressful and is considered more simplistic as typically conducted with catheters. However, home hemodialysis requires more frequent treatment.
Home hemodialysis suffers from still additional disadvantages. Current home hemodialysis systems are big, complicated, intimidating and difficult to operate. The equipment requires significant training. Home hemodialysis systems are currently too large so as to be portable, thereby preventing hemodialysis patients from traveling. Home hemodialysis systems are expensive and require a high initial monetary investment, particularly compared to in-center hemodialysis where patients are not required to pay for the machinery. Present home hemodialysis systems do not adequately provide for the reuse of supplies, making home hemodialysis economically less feasible to medical suppliers. Because of the above mentioned disadvantages, very few motivated patients undertake the drudgery of home hemodialysis.
Currently, most hemodialysis systems employ peristaltic roller pumps which engage flexible tubing to push fluid through a dialysate flow path or blood flow path. These roller pumps are expensive and inefficient. Also troubling, roller pumps for use in hemodialysis can cause damage to blood platelets and introduces the risk of coagulation.
Accordingly, there is a significant need for a hemodialysis system that is transportable, light weight, easy to use, patient friendly and thus capable of in-home use.
Moreover, it would be desirable to provide a home hemodialysis system that possessed no single point of failure in the pumps, motors, tubes, or electronics which would endanger a patient.
Furthermore, it would desirable to provide a hemodialysis system that employed pumps that did not squeeze blood in the blood flow path and did not incorporate flexible materials such as employed with peristaltic roller pumps.
In still an additional aspect, it would desirable to provide a hemodialysis system wherein pump components that came in contact with blood or dialysate could be disposed of after a single patient treatment, but that the pump motor could be reused.
In still an additional aspect, it would be desirable to provide a hemodialysis system that incorporates a reservoir having a flow sensor for measuring the flow of dialysate in the dialysate flow path and which identifies fault conditions in the flow sensor.
Aspects of the present invention fulfill these needs and provide further related advantages as described in the following summary.